1. Field of the Invention
The present invention relates to a radio transmission apparatus and radio transmission method for use in a radio communication system, particularly to a multimode radio transmitter which can be used in a plurality of radio communication systems.
2. Related Background Art
A radio apparatus for use in a radio communication system is divided into a transmission apparatus (hereinafter referred to as a transmitter) used for the radio apparatus to transmit a signal, and a reception apparatus (hereinafter referred to as a receiver) used for receiving the signal sent from another radio apparatus.
There are various types of configurations of the transmitter and receiver, and the most suitable configuration to satisfy system requirement of the radio communication system at which the radio apparatus aims is employed as the configurations of the transmitter. Three types of configurations frequently used as a transmitter configuration will briefly be described hereinafter.
(First Transmitter Configuration: Translation Loop)
FIG. 13 shows a transmitter configuration called “Translation Loop”. The configuration also has other names such as “Modulation Loop”, but here the name “Translation Loop” will be used.
In the “Translation Loop”, since a phase lock loop (PLL) is composed of a phase comparator 5, loop filter 6, first voltage control oscillator 7, frequency converter 8, and second synthesizer 9, an RF oscillator signal outputted from the first voltage control oscillator 7 is a signal having remarkably little noise.
However, the configuration of the “Translation Loop” can be used only in the radio communication system using frequency modulation such as a Gaussian-filtered minimum shift keying (GMSK) modulation.
An operation of the “Translation Loop” will briefly be described hereinafter taking the radio communication system (hereinafter referred to as GSM900) called global system for mobile communication (GSM) using a 900 MHz band as an example.
First, GMSK-modulated base band signals inputted via I and Q channel base band signal input terminals 1, 2 are multiplied with a first local oscillator (LO) signal outputted from a first synthesizer 3 in a quadrature modulator 4, and frequency-converted to an intermediate frequency (IF) signal. Additionally, a 90° phase shifter is omitted (this also applies to all the drawings hereinafter).
Subsequently, the IF signal outputted from the quadrature modulator 4 is inputted into a phase comparator 5.
On the other hand, the first voltage control oscillator 7 outputs a radio frequency (RF) oscillator signal corresponding to a voltage given from a loop filter. The RF oscillator signal outputted from the first voltage control oscillator 7 is inputted into the frequency converter 8. The frequency converter 8 multiplies the RF oscillator signal outputted from the first voltage control oscillator 7 with a second LO signal outputted from the second synthesizer 9, and ideally the frequency of the IF signal outputted form the first voltage control oscillator 7 and the frequency of the IF signal outputted from quadrature modulator is the same. The IF signal outputted from the frequency converter 8 is inputted into the phase comparator 5. The phase comparator 5 compares the phase of the IF signal inputted from the quadrature modulator 4 with that of the IF signal inputted from the frequency converter 8, and outputs a voltage corresponding to a phase difference of the two signals to the loop filter 6. The loop filter 6 attenuates unnecessary high-frequency signals except direct current and low-frequency signals which are generated in accordance with the phase difference of the two IF signals. The first voltage control oscillator 7 outputs the RF oscillator signal corresponding to the voltage outputted from the loop filter 6.
The RF oscillator signal outputted from the first voltage control oscillator 7 is outputted from the first signal output connector for “Translation Loop” 10.
(Second Transmitter Configuration; Super-Heterodyne)
FIG. 14 shows a transmitter configuration called a “Super-Heterodyne”. An operation of the “Super-Heterodyne” will briefly be described hereinafter taking the radio communication system called wide-band code division multiple access (W-CDMA) as an example.
First, the hybrid phase shift keying (HPSK) modulated base band signals are inputted via the I and Q channel base band signal input terminals 1, 2 and multiplied with the first LO signal outputted from the first synthesizer 3 in the quadrature modulator 4, and the IF signals are outputted from the quadrature modulator.
Subsequently, the IF signal outputted from the quadrature modulator 4 is inputted into a first IF variable gain amplifier 11 and the IF signal power is amplified. Next, the IF signals outputted from the first IF variable gain amplifier 11 are inputted into a first IF band pass filter 12, and unnecessary signals in the IF signals are attenuated. The IF signal is inputted into the frequency converter 8. The frequency converter 8 multiplies the IF signal outputted from the first IF band pass filter 12 with the second LO signal outputted from the second synthesizer 9, and outputs the RF signal. The RF signal outputted from the frequency converter 8 is outputted from a signal output terminal 13 for the “Super-Heterodyne”.
The “Super-Heterodyne” can be used regardless of a modulation, and is broadly used in various radio communication systems. Moreover, as the gain dynamic range of the IF variable gain amplifier can be large, the “Super-Heterodyne” is particularly used in the radio communication systems which need a large transmission power control range.
(Third Transmitter Configuration; Direct-Conversion)
FIG. 15 shows a transmitter configuration called “Direct-Conversion”. An operation of the “Direct-Conversion” will be described hereinafter taking the radio communication system called personal digital cellular (PDC) using a frequency of a 800 MHz band as an example.
In this configuration, first, the base band signals inputted via the I and Q channel base band signal input terminals 1, 2 and multiplied with the first LO signal outputted from the first synthesizer 3 in the quadrature modulator 4, in order to frequency-convert to the RF signals.
Subsequently, the RF signal outputted from the quadrature modulator 4 is inputted into a first RF variable gain amplifier 14 to amplify power. Next, the RF signals which are outputted from the first variable gain amplifier for RF 14 and from which the unnecessary signals are removed by a first band pass filter for RF 15 are outputted. The RF signal outputted from the first band pass filter for RF 15 is outputted from a signal output terminal for “Direct-Conversion” 16.
Similarly as the “Super-Heterodyne”, the “Direct-Conversion” can be used regardless of the modulation, and is therefore used for the radio communication systems using various modulation. Moreover, since the amplifier and filter for the IF stage is unnecessary, a transmitter can be miniaturized as compared with “Super-Heterodyne”. Therefore, the “Direct-Conversion” is often used, when the radio apparatus is to be miniaturized.
As described above, for many of the conventional radio apparatuses, the above-described transmitter configurations have been designed exclusively for the respective radio communication systems, and an exclusive-use radio apparatus has been constituted for each radio communication system.
(Multimode Radio Apparatus)
In recent years, cellular phone users have increased all over the world, and various radio communication systems have been used. Therefore, there has been an increasing demand for a so-called “multimode radio apparatus” such that one radio apparatus can be used in a plurality of radio communication systems.
For example, when a transmission section of the “multimode radio apparatus” is realized by a conventional method of constituting the transmitter exclusive for each radio communication system and, for example, when the multimode radio apparatus can be used in three radio communication systems GSM/W-CDMA/PDC, as shown in FIG. 16, the same number of transmitters exclusive for the respective radio communication systems as the number of radio communication systems are arranged, and the transmitters are large-scaled. Additionally, each of the first and second synthesizers 3 and 9 includes the same number of voltage control oscillators as the number of the corresponding radio communication systems.
On the other hand, there has been a demand for a convenient, small-sized and light-weight radio apparatus superior in portability.